Dome headed roof bolt

ABSTRACT

A new bolt head design is disclosed and claimed. The bolt head has a radius between the shaft and the first side of a washer which spreads the shaft load more evenly to the washer. A concave dome is located between the second side of the washer and the driver of the head. These elements more evenly distribute the load, increase the bolt head strength and help prevent the washer, shaft and washer driver interfaces from failing when the bolt is loaded either in a linear or non-linear fashion.

FIELD

The present version of these embodiments relate generally to the field of head designs for bolts or fasteners and more particularly to roof bolts or fasteners used in mining and tunneling underground.

BACKGROUND

These embodiments relate to head designs for roof bolts, and more particularly to a novel head design for the head of bolts used generally in mines and underground digging. Generally when digging underground for mining and other purposes, the roof can become unstable and a many methods have been used to reinforce the roof or ceiling. The roof becomes unstable because the material for the tunnel has been removed. The material above the ceiling can cause the ceiling to crack and fall causing collapse of the tunnel. Many methods to reinforce the ceiling have been developed and practiced to help overcome this potentially dangerous problem.

One method of reinforcing the roof involves drilling a hole into the ceiling and inserting a bolt or rod with plate adjacent to the head to reinforce the ceiling. The shaft of the bolt can be threaded or have ribs along the length of the shaft and some shafts are smooth. The bolt head generally has some type of standard head design so that tools and equipment can attach to the head and drive the bolt. There is a washer element between the head of the bolt and the shaft. The bolt can be very long depending upon the type of material in the ceiling. Miners and underground excavators like to see certain types of material in the ceiling above the tunnels so that bolts and plates can be most effective. Many times the preferred rock material for retaining the shaft to the rock is several feet from the ceiling, in some cases 6-8 feet or even more.

The bolt can be retained in the hole with the threads, with a mechanical anchorage device or can have a grout or adhesive that is inserted at various distances from the head or ceiling but generally at the top end of the hole. The distance for placement of the adhesive is determined by the type of rock that is found along the length of the hole. The adhesive can be placed at some appropriate distance from the head depending upon the type of material found at various elevations above the ceiling.

Many methods have been developed for securing the bolt in the hole. One method involves threaded rods and another involves two part adhesives. Another method involves pumping adhesives or grout through a hole in the shaft of the bolt. The two part adhesives are generally assembled in a separated two part cartridge which can be inserted into the hole before the bolt shaft or along with the bolt shaft. When the bolt shaft is installed, the shaft is spun and this breaks the separation of the two materials in the cartridge and mixes them. The spinning of the bolt causes the adhesive to mix which results in a chemical reaction and results in the binding of the shaft to the rock with the adhesive. An upward force can also be given to the bolt head such that when the adhesive solidifies there is an upward force on the ceiling or the bolt is in tension.

The bolt or rod generally has a plate located adjacent to the washer element of the head of the bolt to disperse the loading of the bolt, head, washer and plate over the surface area of the ceiling adjacent to the plate. The bolt is installed so that the plate is as flush with the ceiling as is possible. The bolt can then be forced upwards to create a tension in the bolt or various other methods have been developed to turn the bolt into the ceiling to tension the bolt. Other methods to tension the bolt either before and after the bolt has been inserted are known in the art. This loading from the bolt, head and washer is transferred to the plate and to the ceiling which compresses the ceiling to support the rock above the ceiling to deter collapse.

There are standards for the design and testing of roof bolts, shafts and heads, some of which are found in ASTM Designation F 432-04 “Standard Specifications for Roof and Rock Bolts and Accessories” and ASTM Designation F 606-90 “Standard Test Methods for Determining the Mechanical Properties of Externally and Internally Threaded Fasteners, Washers and Rivets”.

These standards specify tests to ascertain the minimum loading to which the roof bolts, heads, shafts and plates should withstand. While the products on the market generally meet the tests designed for roof bolts, failures still occur in the real world.

The applicant has seen cases where the washers of the bolt heads become loaded in an unbalanced manner. This is due to the fact that many times the holes in the ceiling are not drilled straight or the ceiling surface is not perpendicular to the holes and plate thereby does not sit parallel and adjacent to the ceiling surface. Other times the bolt is not driven exactly concentric to the hole center line when installed.

When any of these conditions occur, the washer is loaded at the washer plate interface more on one side of the washer than the other. When the load becomes too great, the washer regularly fails and this condition can result in failure of the head and shaft too. Subsequently, the plates can fall away from the ceiling. Failure of the bolt or plate support can result in the loss of ground support, ceiling dropping and possible collapse. If repair is possible it can be extremely costly. Work can stop until the tunnels or digging can be made safe from ceiling collapse.

While these bolts do meet the specifications for roof bolts, failures still occur. In other cases where the bolt load is perpendicular to the washer and plate in the ceiling, these bolts still fail at the washer head interface when the washers concave towards the head end of the bolt or shear from the bolt. The plate then fractures, bends or detaches from the the bolt head resulting in the ceiling lowering or possible collapse.

Applicants sought to change the head design to help prevent the failure of the bolt heads at the washer head interface and washer shaft interface. Applicant has modified the area on the shaft directly below the washer and modified the head between the head end and the washer.

Testing has been performed and it has been found that these new embodiments are stronger by as much as 60% over the roof bolt head designs in the background art.

For the foregoing reasons, there is a need for a new roof bolt head design or a dome headed roof bolt.

SUMMARY

In view of the foregoing disadvantages inherent in the background art of ceiling or roof bolts there is a need for a dome headed roof bolt.

A first objective of these embodiments is to provide a roof bolt that is stronger than the background art.

Another objective of these embodiments is to provide a device that can be installed in the same manner as the background art.

It is yet another objective of these embodiments to provide a device that has increased strength between the shaft and the washer.

It is a still further objective of these embodiments to provide a device that has increased strength between the washer and the driver.

An additional objective of these embodiments is to provide a device that is less likely to fail with off set loading of the bolt and bolt head.

These together with other objectives of these embodiments, along with various features of novelty which characterize these embodiments, are pointed out with particularity in the claims annexed hereto forming a part of this disclosure. For a better understanding of these embodiments, their operating advantages and the specific objectives attained by their uses, reference should be had to the accompanying drawings and descriptive matter in which there is illustrated a preferred embodiment.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 shows a side view of a typical background art roof bolt.

FIG. 2 shows a side view of one embodiment of the applicant's dome headed roof bolt.

FIG. 3 shows a side view of one embodiment of the applicant's bolt installed in the ceiling with a plate.

FIG. 4 shows a top view of one embodiment of the head end of the bolt with indicia.

FIG. 5 shows a top perspective view of one embodiment of the bolt.

FIG. 6 shows a side view of one embodiment of the bolt.

FIG. 7 shows a bottom perspective view of one embodiment of the bolt.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring to the drawings in detail wherein like elements are indicated by like numerals, there is shown in FIG. 1 a side view of typical background art roof bolt. As can be seen, this embodiment has a diameter between the shaft and the washer that is approximately parallel to the shaft. The washer has parallel sides and the interface between the top of the washer and the head end has a small chamfer.

FIG. 2 shows one embodiment of the applicant's roof bolt 12. Applicant's bolt 12 has a shaft 22 with ribs 24. Applicant's bolt 12 shaft 22 could also have threads or the shaft 22 could have a smooth surface finish (not shown). On one end of the shaft 22 is the head 28 and head end 20. It should be understood that applicant's head 28 design could be utilized on other types of bolts 12.

Between the shaft 22 and the washer 18 is an annular radius 26. Annular radius 26 helps distribute any tensile loading of the shaft 22 to the washer 18. As can be seen in FIG. 1, the background art has a relatively constant diameter section immediately between the shaft and the washer and this causes loading over a smaller diameter of the washer as compared to the loading that occurs with applicant's annular radius 26. Applicant's washer 18 can be thicker than the background art also. The background art allows a stress concentration to occur between the shaft and washer and this is where the failure typically occurs.

FIG. 2 shows that between the washer 18 and the driver 14 is a dome 16. The dome 16 angles from the washer 18 to the driver 14 in a concave shape towards the head end 20. The driver 14 is used to install the bolt 12 into the hole 52 in the rock 54, FIG. 3. The driver 14 can also have a hole 38 with a surface 42 for marking indicia 40 indicating various parameters and physical characteristics of the bolt 12 as is well known in the art, FIGS. 4, 5.

To install the bolt 12, the user drills a hole 52 in the rock 54 to a certain depth dependent upon the makeup of the rock 54 found in the hole 52. Generally softer rock 54 requires a deeper hole 52, FIG. 3.

When the hole 52 is drilled to the appropriate depth, the user places a plate 50 over the shaft end 30 of the bolt 12 and slides the plate 50 to the first side 32 of washer 18. A tool can then be placed on the head end 20 of the bolt 12, the shaft end 30 is inserted into the hole 52 in rock 54. A mechanical anchorage device, or adhesive can also be inserted into hole 52 along with the bolt 12 or can be placed prior to the insertion of the bolt 12 depending upon the specific retention method employed by the user.

The driver 14 is generally turned and either the mechanical anchorage device or adhesive secures the shaft 22 to the interior of the hole 52. The plate 50 is secured against the ceiling rock 54 either via the various mechanical anchorage devices, adhesives or grout that secures the shaft 22 to the interior of the hole 52. This places the bolt 12 and plate 50 under load to help secure the rock 54 in the direction of force F, FIG. 3.

The end result of this installation is that the bolt 12 and plate 50 secure the ceiling in an upwards direction in the direction of force F to secure the rock 54 and help prevent collapse of the ceiling into the tunnel and excavated area.

It should be noted that while this discussion focuses on retaining ceiling rock 54, this device could also be used to secure side walls of an excavation.

The applicant's dome headed roof bolt 12 provides better retention of the bolt 12 in the rock 54. Background art when loaded would often fail at the head, primarily the washer shaft interface. Applicant has added an annular radius 26 to the shaft 22, between the shaft 22 and the first side 32 of the washer 18. The diameter of the annular radius 26 is less than the diameter of the washer 18. This radius 26 better distributes the tensile loading that occurs in the shaft 22 and in transferring the load to the head 28. This radius 26 also increases the strength of the shaft 22 and washer 18 interface when the bolt 12 is not loaded in a purely tensile condition or the bolt has a bending condition. This bending condition can result from the bolt hole 52 not being drilled perpendicular to the ceiling. This non-perpendicular hole 52 condition can be due to the drilling in different layers of rock 54 and the bit wandering. This bending condition can also result from irregularities in the surface of the ceiling where the plate 50 is secured. It is also possible that the shaft 22 of the bolt 12 will not be installed in the center of the hole 52. These conditions can cause uneven loading of the washer 18, plate 50 and ceiling resulting in stress concentrations in the washer 18 and head 28 of bolt 12.

Applicant has also added a circular dome 16 to the second side 34 of the washer 18. This dome 16 has a concave shaped surface extending from the second side 34 of the washer 18 towards the head end 20 of the bolt 12. The driver 14 is connected to the dome 16. This dome 16 also increases the strength of the bolt 12 when the bolt 12 is in tension and increases the strength of the bolt 12 when the bolt is not in a purely tensile condition. The dome 16 tends to increase the strength of the connections between the radius 26, washer 18, dome 16 and driver 14. The dome 16 discourages the washer 18 from failing in pure tension and the non-linear loading condition.

It will now be apparent to those skilled in the art that other embodiments, improvements, details and uses can be made consistent with the letter and spirit of the foregoing disclosure and within the scope of this application, which is limited only by the following claims, construed in accordance with the patent laws, including the doctrine of equivalents. 

1. A bolt for attaching plates to the interior of excavations, the bolt comprising: a shaft, the shaft having a shaft end and the opposite end of the shaft terminating in an annular radius, the radius attached to a first side of a washer, a second side of the washer attached to a dome, the dome extending in a concave manner away from the washer, the dome attached to a driver, the driver having a hole and the hole having a surface and indicia located on the surface.
 2. The bolt of claim 1, further comprising: ribs extending along the shaft from near the radius to near the shaft end.
 3. The bolt of claim 1, further comprising: threads located on the shaft between the radius and the shaft end.
 4. A bolt for attaching plates to the interior of an excavation, the bolt comprising: a driver, the driver attached to a concave shaped dome, a hole in a head end of the driver, the hole terminating in a surface, indicia located on the surface; a washer, the washer having a first side and a second side; the dome terminating at the second side of the washer, the first side of the washer attached to an annular radius having a diameter less than that of the washer; the radius joining the first side of the washer to a shaft, the shaft terminating in a shaft end; and a plurality of ribs extending along the shaft from near the radius to near the shaft end.
 5. The bolt of claim 4, further comprising: the ribs replaced by threads located between the radius and the shaft end.
 6. A head for a bolt, the head comprising: a driver, the driver having a hole with a surface, indicia located on the surface; the driver attached to a dome, the dome having a concave shape and extending towards the driver from a second side of a washer, the washer having a first side, the first side adjacent to an annular radius, the radius joined to a shaft, the shaft having a shaft end; and whereby the radius provides a transition from the diameter of the shaft to the first side of the washer.
 7. The bolt of claim 6, further comprising: ribs extending along the shaft from near the radius to near the shaft end.
 8. The bolt of claim 7, further comprising: threads located on the shaft between the radius and the shaft end.
 9. A dome headed bolt for roof bolts, the bolt comprising: a driver on one end of the bolt, the driver adjacent to a dome which extends in a concave manner from a washer towards the driver, the dome terminating in a diameter that matches the diameter of a second side of the washer, the washer having a first side, an annular radius attached to the first side of the washer, the annular radius attached to a shaft and the shaft having a shaft end and ribs located on the shaft from the radius to the shaft end.
 10. The dome headed roof bolt of claim 9, further comprising: the driver having a hole with a surface and indicia on the surface.
 11. The dome headed roof bolt of claim 9, further comprising: the ribs replaced by threads.
 12. The dome headed roof bolt of claim 9, further comprising: the shaft surface is smooth with no ribs. 